The human spine is a biomechanical structure with thirty-three vertebral members, and is responsible for protecting the spinal cord, nerve roots and internal organs of the thorax and abdomen. The spine also provides structure support for the body while permitting flexibility of motion. A significant portion of the population will experience back pain at some point in their lives resulting from a spinal condition. The pain may range from general discomfort to disabling pain that immobilizes the individual. Back pain may result from a trauma to the spine, be caused by the natural aging process, or may be the result of a degenerative disease or condition.
The intervertebral disc functions to stabilize the spine and to distribute forces between vertebral bodies. A normal disc includes a gelatinous nucleus pulposus, an annulus fibrosis and two vertebral endplates. The nucleus pulposus is surrounded and confined by the annulus fibrosis between the vertebral endplates.
It is known that intervertebral discs are prone to injury and degeneration. For example, herniated discs are common, and typically occur when normal wear, or exceptional strain, causes a disc to rupture. Degenerative disc disease typically results from the normal aging process, in which the tissue gradually looses its natural water and elasticity, causing the degenerated disc to shrink and possibly rupture.
Intervertebral disc injuries and degeneration are frequently treated by replacing or augmenting the existing disc material. Current intervertebral disc replacement procedures tend to utilize full-sized implants, particularly hydrogels, to augment or replace the original disc nucleus. These materials are commonly implanted after first making a hole with a guide wire, and then subsequently enlarging the hole with a succession of sleeves having increased diameters. Alternatively, a larger hole may be made by surgical incision, using a scalpel or a small diameter coring blade.
One problem with such implants is that they require a relatively large hole to be cut in the disc annulus to allow introduction of the implant. Since the hole must be large enough to accommodate a full sized implant, the annulus must be plugged or sewn closed after implantation to avoid allowing the implant to be expelled from the disc. This complicates the procedure, adding surgical time and cost, and leaving a less sound annulus when the procedure is complete.
Another problem with such implants is the possibility of tearing or otherwise damaging the hydrogel implant during implantation. Moreover, once positioned in the disc space, many hydrogel implants may migrate in the disc space and/or may be expelled from the disc space through an annular defect, or other annular opening.
A need therefore exists for more durable implants, as well as implants that are resistant to migration and/or expulsion through an opening in the annulus fibrosis. The devices and methods disclosed herein address these needs.